Transportation Vehicle

The present invention relates to a transportation vehicle such as a dump truck that is provided with a cooling fan.

A transportation vehicle provided with a cooling fan is known (see Patent Document 1). A cooling air generated by the cooling fan cools a cooling object such as engine cooling water. Patent Document 1 discloses a controller that performs first control for setting the rotational speed of the cooling fan according to the temperature of the cooling object when the temperature of the cooling object is higher than a lower limit threshold temperature and second control for setting the rotational speed of the cooling fan to a minimum rotational speed and making the cooling fan perform a reverse rotation when the temperature of the cooling object is lower than the lower limit threshold temperature.

In the transportation vehicle such as a dump truck, a heat exchanger such as a radiator and the cooling fan may be arranged in a front portion of a vehicle body. In addition, a load on the transportation vehicle at a time of travelling changes according to the presence or absence of a cargo, a road gradient, and the like. For example, unloaded travelling, level ground travelling, and the like are low-load travelling states as compared with cargo travelling, uphill travelling, and the like. When the cooling fan continues to generate the cooling air in a low-load travelling state, the cooling air and a travelling wind may overcool the cooling object (such as the engine cooling water). Accordingly, stopping the cooling fan is considered in order to prevent the overcooling. As a method for stopping the cooling fan, a method of interrupting the supply of a hydraulic operating fluid from a hydraulic fluid source such as a hydraulic pump to a hydraulic motor that drives the cooling fan is considered.

In the vehicle described in Patent Document 1, a control valve (switching valve) that switches a supply destination of the hydraulic operating fluid, which is supplied from the hydraulic fluid source, to a fan control valve or to a cargo handling device is provided on an upstream side of the fan control valve that controls the rotational direction of the fan. That is, in the vehicle described in Patent Document 1, the hydraulic fluid source is shared between the cargo handling device and the hydraulic motor of the cooling fan.

Hence, with the configuration described in Patent Document 1, the overcooling can be prevented by, for example, switching the supply destination of the hydraulic operating fluid, which is supplied from the hydraulic fluid source, to the cargo handling device, and thereby stopping the cooling fan in a low-load travelling state. However, there arises such a problem that a plurality of control valves are provided to a hydraulic circuit, and the hydraulic circuit has a complex configuration.

It is an object of the present invention to provide a transportation vehicle that can prevent an overcooling of a cooling object with a simple configuration.

A transportation vehicle according to one aspect of the present invention includes: at least one hydraulic pump that is driven by a prime mover; a hydraulic motor that is driven by a hydraulic operating fluid supplied from a first hydraulic pump of the at least one hydraulic pump; a cooling fan that is driven by the hydraulic motor; a heat exchanger that is disposed in a front portion of a vehicle body, and cools a cooling object by cooling air generated by the cooling fan; a hydraulic cylinder that is driven by the hydraulic operating fluid supplied from the first hydraulic pump; a fan control valve that controls a flow of the hydraulic operating fluid supplied from the first hydraulic pump to the hydraulic motor; a cylinder control valve that controls a flow of the hydraulic operating fluid supplied from the first hydraulic pump to the hydraulic cylinder; and a controller that controls the fan control valve and a delivery capacity of the at least one hydraulic pump. In the transportation vehicle, the fan control valve and the cylinder control valve are connected in tandem to a hydraulic fluid line that connects the first hydraulic pump and a hydraulic operating fluid tank to each other. In addition, the fan control valve is disposed on an upstream side of the cylinder control valve, and the fan control valve has a neutral position that makes the first hydraulic pump and the cylinder control valve communicate with each other, interrupts communication between the first hydraulic pump and the hydraulic motor, and makes a suction port and a delivery port of the hydraulic motor and the hydraulic operating fluid tank communicate with each other, and further, the fan control valve has a rotation position that interrupts the communication between the first hydraulic pump and the cylinder control valve, makes the first hydraulic pump and the suction port of the hydraulic motor communicate with each other, and makes the delivery port of the hydraulic motor and the hydraulic operating fluid tank communicate with each other.

According to the present invention, it is possible to provide a transportation vehicle that can prevent an overcooling of a cooling object with a simple configuration.

A transportation vehicle according to a first embodiment of the present invention will be described with reference to the drawings.is a perspective view illustrating an external appearance of a dump truckas an example of the transportation vehicle according to the first embodiment of the present invention. In the following description, unless otherwise specified, a forward direction of a cab seat (left front direction; see an arrow in the figure) is a forward direction of a vehicle body.

The dump truckillustrated inis a large-sized dump truck for operating at a mine or the like. The dump truckincludes a vehicle body, a cab, a bed, front wheels, and rear wheels. The cabis supported by a supporting base, and is located on a front side and a left side on the vehicle body. The cabforms an operation room that an operator of the dump truckboards and alights from. Provided within the cabare a cab seat, an accelerator pedal, a brake pedal, a steering wheel for steering (none is illustrated), an operation device(see) for the bed, and the like.

The bedis raisably and lowerably mounted on a rear portion of the vehicle body. The bedis rotatably supported by a rear side of the vehicle bodyvia a coupling pin, and is moved vertically with the coupling pin as a pivot by an extending or contracting action of hoist cylinders(see). The front wheelstravellably support the vehicle bodyat a left and a right of a front portion of the vehicle body, and the rear wheelstravellably support the vehicle bodyat a left and a right of a rear portion of the vehicle body. The front wheelsconstitute steered wheels to be steered by the operator of the dump truck(steering operation). The rear wheelsconstitute driving wheels of the dump truck. The rear wheelsare rotationally driven by a travelling driving device (not illustrated).

A front surface of the vehicle bodyis provided with a front grille. The front grilleis provided with a plurality of air holes for taking outside air into the inside of the vehicle body.

is a plan schematic view illustrating a configuration of the dump truck. As illustrated in, mounted within the vehicle bodyare an engine, a generatorconnected to the engine, a plurality of hydraulic pumps connected to the engine, a cooling fanfor generating cooling air, and a radiatoras a heat exchanger for cooling engine cooling water by the cooling air generated by the cooling fan. The engine cooling water is a refrigerant for cooling the engine, and is a cooling object to be cooled by the cooling air generated by the cooling fan. Incidentally, whileillustrates only the radiatoras a heat exchanger, a heat exchanger such as an oil cooler for cooling a hydraulic operating fluid may be mounted.

The engineas a prime mover is constituted by, for example, a large-sized diesel engine. The cooling fanis driven by a fan motor(see) to be described later. The cooling fansucks in outside air from the front side of the vehicle bodythrough the front grille, and generates the cooling air that flows from the front side of the vehicle bodyto the rear side thereof (see arrow F). The radiatoris disposed on the rear side of the front grille. The radiatoris therefore cooled by the cooling air.

The radiatorperforms heat exchange with the cooling air (air) generated by the cooling fan, and thereby cools the engine cooling water heated by the engine. The engine cooling water cooled by the radiatorreturns to the engine, and cools the engine. Incidentally, the radiatoris disposed in the front portion of the vehicle body, and therefore receives a travelling wind (see an arrow F). Hence, the engine cooling water within the radiatoris cooled not only by the cooling air but also by the travelling wind.

A hydraulic systemof the dump truckwill be described with reference to. As illustrated in, the hydraulic systemof the dump truckincludes: a variable displacement type hydraulic pump (hereinafter written as a first hydraulic pump)and a fixed displacement type hydraulic pump (hereinafter written as a pilot pump)that are driven by the engine; a pair of hoist cylinders (only one hoist cylinder is illustrated in)that are driven by the hydraulic operating fluid supplied from the first hydraulic pump; a fan motorthat is driven by the hydraulic operating fluid supplied from the first hydraulic pump; a hydraulic operating fluid tankthat stores the hydraulic operating fluid; a fan control valveand a hoist control valvethat are provided on a center bypass line CL as a hydraulic fluid line that connects the first hydraulic pumpand the hydraulic operating fluid tankto each other; and a controllerthat controls various parts of the dump truck.

The first hydraulic pump (main pump)sucks in the hydraulic operating fluid from the hydraulic operating fluid tankand delivers a high-pressure hydraulic operating fluid (pressurized fluid), by being driven by the engine. A delivery port of the first hydraulic pumpis connected to the hydraulic operating fluid tankvia the center bypass line CL. The fan control valveand the hoist control valveare connected in tandem with each other along the center bypass line CL. The fan control valvecontrols a flow of the hydraulic operating fluid supplied from the first hydraulic pumpto the fan motorand a flow of the hydraulic operating fluid discharged from the fan motorto the hydraulic operating fluid tank. The hoist control valveis a cylinder control valve that controls a flow of the hydraulic operating fluid supplied from the first hydraulic pumpto the hoist cylinderand a flow of the hydraulic operating fluid discharged from the hoist cylinderto the hydraulic operating fluid tank.

The fan control valveis connected with a supply hydraulic fluid linethat branches from the center bypass line CL. The hoist control valveis provided on a downstream side of the fan control valveon the center bypass line CL. The hoist control valveis connected with a supply hydraulic fluid linethat branches from the center bypass line CL. A return oil from the fan motoris discharged into the hydraulic operating fluid tankthrough a return hydraulic fluid line. A return oil from the hoist cylinderis discharged into the hydraulic operating fluid tankthrough a return hydraulic fluid line.

The fan motoris a hydraulic motor that rotationally drives the cooling fan. An inlet and an outlet (a suction port and a delivery port) of the fan motorare connected to the fan control valveby a pair of motor hydraulic fluid linesand. The pair of motor hydraulic fluid linesandis each connected to the first hydraulic pumpand the hydraulic operating fluid tankvia the fan control valve.

The motor hydraulic fluid lineis connected with a relief valvethat defines a maximum pressure of the motor hydraulic fluid line. The motor hydraulic fluid lineis provided with a relief valvethat defines a maximum pressure of the motor hydraulic fluid line. When pressure within the pair of motor hydraulic fluid linesandexceeds a predetermined value, the pair of relief valvesandlets the hydraulic operating fluid escape to the hydraulic operating fluid tank, and thereby protects hydraulic equipment of a fan circuit including the pair of motor hydraulic fluid linesand.

A pair of check valvesandfor makeup is provided between the pair of motor hydraulic fluid linesandand the return hydraulic fluid line. The check valveis a check valve that allows a flow of the hydraulic operating fluid from the return hydraulic fluid lineto the motor hydraulic fluid line, and inhibits a flow of the hydraulic operating fluid from the motor hydraulic fluid lineto the return hydraulic fluid line. The check valveis a check valve that allows a flow of the hydraulic operating fluid from the return hydraulic fluid lineto the motor hydraulic fluid line, and inhibits a flow of the hydraulic operating fluid from the motor hydraulic fluid lineto the return hydraulic fluid line.

When a negative pressure occurs within the motor hydraulic fluid lineor the motor hydraulic fluid linein a case where the fan motorperforms inertial rotation or in a case where the fan motoris rotated by the travelling wind, the pair of check valvesandresupplies the hydraulic operating fluid within the hydraulic operating fluid tankinto the motor hydraulic fluid linesandhaving a negative pressure through the return hydraulic fluid line.

The hoist cylinderis provided between the vehicle body(see) and the bed(see). The hoist cylinderis a single-stage or multi-stage hydraulic cylinder that raises and lowers the bed. Incidentally,illustrates a two-stage hoist cylinder. The hoist cylinderillustrated inincludes: an outer cylinder portionon the outside; an inner cylinder portionthat is slidably provided within the outer cylinder portionand demarcates the inside of the outer cylinder portioninto a bottom side oil chamberon an upper side and a rod side oil chamberon a lower side; and a piston rodextendably and contractably provided within the inner cylinder portion

The hoist cylinderis extended when the hydraulic operating fluid (pressurized fluid) delivered from the first hydraulic pumpis supplied to the bottom side oil chamberand the hydraulic operating fluid (return oil) is discharged from the rod side oil chamber. When the hoist cylinderis extended, the bedis rotated upward with the coupling pin as a pivot. When the rotating operation is completed, the bedis set in a soil discharge posture inclined obliquely rearward and downward. The hoist cylinderis contracted when the hydraulic operating fluid (pressurized fluid) delivered from the first hydraulic pumpis supplied to the rod side oil chamberand the hydraulic operating fluid (return oil) is discharged from within the bottom side oil chamber. When the hoist cylinderis contracted, the bedis rotated downward with the coupling pin as a pivot. When the rotating operation is completed, the bedis in a laid transportation posture.

The bottom side oil chamberand the rod side oil chamberof the hoist cylinderare connected to the hoist control valveby a pair of actuator hydraulic fluid linesand. The pair of actuator hydraulic fluid linesandis connected to the first hydraulic pumpand the hydraulic operating fluid tankvia the hoist control valve. The actuator hydraulic fluid lineis connected to the bottom side oil chamberof the hoist cylinder. The actuator hydraulic fluid lineis connected to the rod side oil chamberof the hoist cylinder.

The fan control valveis constituted by, for example, a six-port three-position hydraulic pilot type directional control valve. The fan control valveis formed by using a single directional control valve, and has hydraulic pilot portionsandon both of a left side and a right side thereof.

The fan control valveis a selector valve in which a spool (valve disc) can be switched to a normal rotation position (F), a reverse rotation position (R), and a neutral position (N). During a normal time, both of the hydraulic pilot portionsandof the fan control valveare connected to the hydraulic operating fluid tank, and the spool of the fan control valveis retained in the neutral position (N) by centering springs.

When the spool of the fan control valveis in the neutral position (N), an upstream side and a downstream side of the fan control valvein the center bypass line CL communicate with each other, and the communication of the supply hydraulic fluid linewith the motor hydraulic fluid linesandis interrupted. That is, in the neutral position (N), the first hydraulic pumpand the hoist control valvecommunicate with each other, and communication between the first hydraulic pumpand the fan motoris interrupted. The hydraulic operating fluid delivered from the first hydraulic pumpis thereby supplied to the hoist control valvethrough the fan control valve. In addition, when the spool of the fan control valveis in the neutral position (N), a communication lineof the fan control valveconnects the pair of motor hydraulic fluid linesandto each other, and connects the pair of motor hydraulic fluid linesandto the return hydraulic fluid line. In the neutral position (N), the suction port and the delivery port of the fan motorand the hydraulic operating fluid tankcommunicate with each other via the communication line, so that rotation of the cooling fanby an external force is allowed.

When the spool of the fan control valveis in the normal rotation position (F), the supply hydraulic fluid lineand the motor hydraulic fluid linecommunicate with each other, and the motor hydraulic fluid lineand the return hydraulic fluid linecommunicate with each other. That is, in the normal rotation position (F), the communication between the suction port and the delivery port of the fan motorand the hydraulic operating fluid tankvia the communication lineis interrupted, the suction port of the fan motorand the first hydraulic pumpcommunicate with each other, and the delivery port of the fan motorand the hydraulic operating fluid tankcommunicate with each other. Thus, the hydraulic operating fluid delivered from the first hydraulic pumpis supplied to the fan motorthrough the supply hydraulic fluid lineand the motor hydraulic fluid line, so that the fan motorrotates in a normal rotation direction. The hydraulic operating fluid discharged from the fan motoris discharged into the hydraulic operating fluid tankthrough the motor hydraulic fluid lineand the return hydraulic fluid line. When the spool of the fan control valveis in the reverse rotation position (R), the supply hydraulic fluid lineand the motor hydraulic fluid linecommunicate with each other, and the motor hydraulic fluid lineand the return hydraulic fluid linecommunicate with each other. That is, in the reverse rotation position (R), the communication between the suction port and the delivery port of the fan motorand the hydraulic operating fluid tankvia the communication lineis interrupted, the suction port of the fan motorand the first hydraulic pumpcommunicate with each other, and the delivery port of the fan motorand the hydraulic operating fluid tankcommunicate with each other. Thus, the hydraulic operating fluid delivered from the first hydraulic pumpis supplied to the fan motorthrough the supply hydraulic fluid lineand the motor hydraulic fluid line, so that the fan motorrotates in a reverse rotation direction as a direction opposite from the normal rotation direction. The hydraulic operating fluid discharged from the fan motoris discharged into the hydraulic operating fluid tankthrough the motor hydraulic fluid lineand the return hydraulic fluid line.

Thus, the normal rotation position (F) and the reverse rotation position (R) are rotation positions at which the first hydraulic pumpand the fan motorare made to communicate with each other, and the fan motoris rotated by the hydraulic operating fluid delivered from the first hydraulic pump. Incidentally, when the spool of the fan control valveis in a rotation position (F) or (R), the communication between the first hydraulic pumpand the hoist control valvevia the center bypass line CL is interrupted.

The hoist control valveis constituted by, for example, a six-port three-position hydraulic pilot type directional control valve. The hoist control valveis formed by using a single directional control valve, and has hydraulic pilot portionsandon both of a left side and a right side thereof.

The hoist control valveis a selector valve in which a spool (valve disc) can be switched to a raising position (R), a lowering position (L), and a neutral position (N). During a normal time, both of the hydraulic pilot portionsandof the hoist control valveare connected to the hydraulic operating fluid tank, and the spool of the hoist control valveis retained in the neutral position (N) by centering springs.

When the spool of the hoist control valveis in the neutral position (N), communication of the supply hydraulic fluid lineand the return hydraulic fluid linewith the actuator hydraulic fluid linesandis interrupted. This stops the supply of the hydraulic operating fluid to the hoist cylinderand the discharge of the hydraulic operating fluid from the hoist cylinder. The movement of the hoist cylinderis therefore stopped. In addition, when the spool of the hoist control valveis in the neutral position (N), an upstream side and a downstream side of the hoist control valvein the center bypass line CL communicate with each other.

When the spool of the hoist control valveis in the raising position (R), the supply hydraulic fluid lineand the actuator hydraulic fluid linecommunicate with each other, and the actuator hydraulic fluid lineand the return hydraulic fluid linecommunicate with each other. Incidentally, the communication between the upstream side and the downstream side of the hoist control valvein the center bypass line CL is interrupted. Thus, when the fan control valveis in the neutral position (N), the hydraulic operating fluid delivered from the first hydraulic pumpis supplied to the bottom side oil chamberof the hoist cylinderthrough the supply hydraulic fluid lineand the actuator hydraulic fluid line. In addition, the hydraulic operating fluid within the rod side oil chamberis discharged into the hydraulic operating fluid tankthrough the actuator hydraulic fluid lineand the return hydraulic fluid line. The hoist cylinderis thereby driven in an extending direction, that is, in a direction of raising the bed.

When the spool of the hoist control valveis in the lowering position (L), the supply hydraulic fluid lineand the actuator hydraulic fluid linecommunicate with each other, and the actuator hydraulic fluid lineand the return hydraulic fluid linecommunicate with each other. Incidentally, the communication between the upstream side and the downstream side of the hoist control valvein the center bypass line CL is interrupted. Thus, when the fan control valveis in the neutral position (N), the hydraulic operating fluid delivered from the first hydraulic pumpis supplied to the rod side oil chamberof the hoist cylinderthrough the supply hydraulic fluid lineand the actuator hydraulic fluid line. In addition, the hydraulic operating fluid within the bottom side oil chamberis discharged into the hydraulic operating fluid tankthrough the actuator hydraulic fluid lineand the return hydraulic fluid line. The hoist cylinderis thereby driven in a contracting direction, that is, in a direction of lowering the bed.

The pilot pumpis connected to a plurality of solenoid valvestovia a pilot hydraulic fluid line. The pilot hydraulic fluid line between the pilot pumpand the plurality of solenoid valvestois provided with a pilot relief valvethat defines the pressure of the pilot hydraulic fluid line. The plurality of solenoid valvestoare a pressure reducing valve that reduces the pressure of the pilot hydraulic fluid line (primary pressure) according to a control current from the controller, and outputs a pressure after the pressure reduction (secondary pressure) as a pilot pressure. When a control current for standby as an OFF signal is input to the solenoid valvesto, the solenoid valvestomake the hydraulic pilot portions,,, andcommunicate with the hydraulic operating fluid tank. When a control current for driving as an ON signal is input to the solenoid valvesto, the solenoid valvestooutput generated pilot pressures to the hydraulic pilot portions,,, and

The solenoid valvesandfor driving the fan control valveoperate in response to a control command (control current) output from the controllerso as to correspond to the temperature of the engine cooling water. The solenoid valvesandfor driving the hoist control valveoperate in response to a control command (control current) output from the controllerso as to correspond to operation of the operation devicefor the bed.

The controlleris constituted by a computer including a processing devicesuch as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), and a DSP (Digital Signal Processor), a nonvolatile memorysuch as a ROM (Read Only Memory), a flash memory, and a hard disk drive, a volatile memoryreferred to as what is called a RAM (Random Access Memory), an input-output interface, and other peripheral circuitry. These pieces of hardware cooperate with each other to make software operate, and thereby implement a plurality of functions. Incidentally, the controllermay be constituted by one computer, or may be constituted by a plurality of computers.

The nonvolatile memorystores a program capable of performing various kinds of computations and data (data tables, threshold values, equations, and the like) used for the various kinds of computations. That is, the nonvolatile memoryis a storage medium (storage device) from which the program for implementing functions of the present embodiment is readable. The volatile memoryis a storage medium (storage device) that temporarily stores a result of computation by the processing deviceand a signal input from the input-output interface. The processing deviceis a device that expands the program stored in the nonvolatile memoryinto the volatile memory, and executes the program by computation. The processing deviceperforms predetermined computation processing on data taken in from the input-output interface, the nonvolatile memory, and the volatile memory, according to the program.

The input-output interface of the controlleris connected with the operation devicefor performing switching operation of the hoist control valve. The operation deviceis constituted by an electric lever device, for example, and has an operation leverthat is manually tilted by the operator within the cab. The operation deviceis operated to one of a neutral position, a raising position, and a lowering position corresponding to the respective switching positions of the hoist control valve, that is, the neutral position (N), the raising position (R), and the lowering position (L). The operation deviceoutputs an operation signal according to an operation position to the controller.

A temperature sensoris connected to the input-output interface of the controller. The temperature sensorsenses the temperature of the engine cooling water flowing through a cooling water systemof the engine, and outputs a signal indicating a result of the sensing to the controller. The cooling water systemincludes: a cooling water tankthat stores the engine cooling water; a cooling water circulation pumpthat sucks the engine cooling water within the cooling water tankand delivers the engine cooling water; and the radiatorthat cools the engine cooling water by the cooling air. The cooling water systemis a circulation system that can circulate the engine cooling water within the system by the cooling water circulation pump. The engine cooling water cools a cooling target objectsuch as the engineby absorbing the heat of the cooling target object. The engine cooling water rises in temperature by receiving heat from the cooling target object. The engine cooling water that has risen in temperature is cooled in the radiatorby the cooling air generated by the cooling fan. The temperature sensoris, for example, provided to the cooling water tankor a line on a suction side of the cooling water circulation pumpto sense the temperature of the engine cooling water supplied to the radiator.

An input unit of the input-output interface converts signals input from various kinds of devices (the operation device, the temperature sensor, and the like) into data that can be subjected to computation by the processing device. In addition, an output unit of the input-output interface generates signals for output according to results of computation in the processing device, and outputs the signals to various kinds of devices (the solenoid valvesto, a regulator, and the like).

The controlleroutputs a control signal to the regulatorof the first hydraulic pump. The regulatoris a capacity control system that variably controls the displacement volume (delivery capacity per rotation) of the first hydraulic pump. When the first hydraulic pumpis a swash plate type piston pump, for example, the regulatorincludes: a tilting actuator that controls the tilting angle (displacement volume) of a swash plate of the first hydraulic pump; and a solenoid proportional valve that generates a control pressure of the tilting actuator with a delivery pressure of the first hydraulic pumpas a source pressure.

The controllercontrols the fan control valve, when the operation deviceis operated to the neutral position, on the basis of a temperature Tc of the engine cooling water (which temperature will hereinafter be described also as a cooling water temperature) sensed by the temperature sensor. Details of control of the fan control valvewill be described later.

The controllerretains the hoist control valvein the neutral position (N) when the operation deviceis operated to the neutral position. That is, the controlleroutputs an OFF signal to both of the solenoid valvesand.

The controllerperforms control to switch the hoist control valveto the raising position (R) when the operation deviceis operated to the raising position. That is, the controlleroutputs an ON signal to the solenoid valve, and outputs an OFF signal to the solenoid valve. Thus, a pilot pressure generated by the solenoid valveacts on the hydraulic pilot portionto switch the hoist control valveto the raising position (R). When the operation deviceis operated to the lowering position, the controllerperforms control to switch the hoist control valveto the lowering position (L). That is, the controlleroutputs an OFF signal to the solenoid valve, and outputs an ON signal to the solenoid valve. Thus, a pilot pressure generated by the solenoid valveacts on the hydraulic pilot portionto switch the hoist control valveto the lowering position (L).

The controllercontrols rotation and stopping of the fan motorand a rotational direction of the fan motorby controlling a switching position of the fan control valve. In addition, the controllercontrols a rotational speed of the fan motorby controlling a delivery capacity q of the first hydraulic pumpin a range from a minimum capacity qmin to a maximum capacity qmax via the regulator. Referring to, description will be made of functions of the controllerwhich functions are related to control of the cooling fanand the first hydraulic pump.is a functional block diagram of the controller. As illustrated in, the controllerfunctions as a determining section, a valve control section, and a pump control sectionby executing the program stored in the nonvolatile memory.

As illustrated in, the determining sectiondetermines whether the cooling water temperature Tc sensed by the temperature sensoris equal to or higher than a first threshold value Tc. In addition, the determining sectiondetermines whether the cooling water temperature Tc sensed by the temperature sensoris equal to or higher than a second threshold value Tc. The first threshold value Tcand the second threshold value Tcare stored in the nonvolatile memoryin advance. A magnitude relation between the first threshold value Tcand the second threshold value Tcis Tc<Tc. When the cooling water temperature Tc is lower than the first threshold value Tc, the determining sectiondetermines that a condition for stopping the cooling fanis satisfied. Hence, the first threshold value Tccan be said to be a threshold value for determining whether to stop the driving of the cooling fan.

The valve control sectioncontrols the switching position of the fan control valveon the basis of a determination result of the determining section. When the determining sectiondetermines that the condition for stopping the cooling fanis not satisfied, the valve control sectionoutputs an ON signal to the solenoid valveand outputs an OFF signal to the solenoid valve, and thereby switches the fan control valveto the normal rotation position (F). When the fan control valveis switched to the normal rotation position (F), the supply hydraulic fluid lineand the motor hydraulic fluid linecommunicate with each other, and the motor hydraulic fluid lineand the return hydraulic fluid linecommunicate with each other. Thus, the fan motoris rotated by the hydraulic operating fluid supplied from the first hydraulic pump.